The present invention relates to a flat electrolytic capacitor having interleaved aluminum anode and cathode foils in an enclosure containing electrolyte.
For high frequency applications a flat capacitor is desirable because it can achieve lower impedance than foils wound in a coil to form a cylindrical capacitor. Canadian Patent No. 1,002,133 discloses a flat capacitor having interleaved anode and cathode foils in a stack. At least the anode foils are anodized, and the edges are deformed during cold welding to an aluminum lead in order to displace the oxide formed in the anodizing process. Only aluminum leads are disclosed. While the patent states that the casing may be filled with electrolyte and sealed, this prohibits the use of copper leads, because the weld joints are necessarily in the casing, and the electrolyte attacks and dissolves copper. As such an electrolytic capacitor having copper leads cannot be achieved. This is a disadvantage, because aluminum cannot be soldered. Therefore an electrolytic capacitor according to this patent cannot be directly soldered to a printed circuit board.
In power supplies such as ballasts for lamps and battery chargers, capacitors are necessary for power balancing between a 50 Hz or 60 Hz input and a load which requires a constant voltage output. Lower parasitic inductance is not especially important for these applications because frequencies are low. However using a flat capacitor would be advantageous to miniaturize the ballast or other power converters. Thus it would be advantageous to be able to solder the leads to a printed circuit board.